1. Field of the Invention
The present invention relates to a rotary cutter for a mowing machine for mowing grass or the like by a cord (generally made of nylon) which is drawn out in a radial direction of a case which is driven through a rotary shaft by a driving power of a motor or the like, and more particularly, to the rotary cutter of a type that the cord will be automatically drawn out in case where the cord has been worn out and become short.
2. Background Art
Conventionally, it has been a mainstream method in the rotary cutter of this type that a nylon cord is contained in a reel, and for the purpose of drawing out the cord when the cord has been worn out, the cord will be drawn out by pressing the cutter to the ground during rotation, striking the cutter, or increasing rotation speed of the cutter. However, the method of drawing out the cord by pressing the cutter to the ground or by striking the cutter has been dangerous, because small stones may be scattered. Moreover, the method of increasing the rotation speed has incurred a complicated structure and an increase of weight, and the cord had to be drawn out by increasing the rotation speed to the highest. Therefore, both the methods have had such problems that the motor which is a power source and the cutter have been subjected to excessive strain, and it has been unstable and very dangerous to draw out the cord.
In order to solve the above described problems, the applicant has already proposed a rotary cutter employing such a method that the cord will be automatically drawn out of the reel, when the cord has been worn out and become short during mowing work (Reference should be made to JP-A-5-168328). This method has the following advantageous features. When a drawn length of the cord has become short, the cord will be automatically drawn out with a change of centrifugal force, even during the work, and therefore, the above described operation such as pressing or striking the cutter, or increasing the rotation speed is not required. In addition, exchange of the cord can be easily and safely conducted, because the structure is simple.